1. Field of the Invention
The present invention relates to a Fresnel lens sheet that scarcely makes the projected image distorted, to a rear projection screen, and to a rear-projection-type display.
2. Background Art
A projection television, or a rear-projection-type display, comprises a rear projection screen on which imaging light from a light source that has been spread is projected. This rear projection screen is usually composed of: a Fresnel lens element for refracting the imaging light from the light source that has been spread and projected on the Fresnel lens element, to make the light parallel or almost parallel and emitting this light toward the viewer side; and a lenticular lens element for scattering the parallel or almost parallel light emerging from the Fresnel lens element to provide an image to viewers who are in a wide area. Although a CRT light source of three-tube type by which light of three primary colors are projected from three different tubes has been usually used as the light source in a rear-projection-type display of the above-described type, a light source of single-tube type, using an LCD or DLP, has come to be used as well in recent years.
As shown in FIG. 16, the mode of a conventional rear-projection-type display 52 has generally been that imaging light 5 emitted from a single-tube-type light source 8 is made to reflect from a mirror 53 and then to enter a rear projection screen 10 vertically or almost vertically to its center. Therefore, as shown in FIG. 17, the position of the rear projection screen 10 has not affected the projected image whether the screen is brought near or moved away from the light source 8 in the direction in which the imaging light 5 is incident on the rear projection screen 10.
Rear-projection-type displays that are made much thinner than ever by letting the imaging light 5 enter the rear projection screen 10 obliquely to its center have been proposed in recent years. Namely, there has been proposed a mode that the imaging light 5 emitted from the light source 8 is made to reflect from the mirror 53 and then to enter the rear projection screen 10 obliquely to its center, like in a rear-projection-type display 51 shown in FIG. 5. In the rear projection screen 10 contained in such a rear-projection-type display 51, it has been proposed to use a Fresnel lens sheet (see FIG. 12B) having a Fresnel lens of total reflection type (total reflection Fresnel lens) (see Japanese Laid-Open Patent Publication No. 208041/1986, for example).